This seems like something I would enjoy doing, but ultimately fail at... Maybe just maybe, I may have the attention span to finish the map using the default terrains and such. (is there a wide variety of terrains available by default?)
I would really enjoy using the bridge tool, especially making trees walkable and such (must we place the tree, for example across a chasm then make it walkable or just draw a bridge and have it spawn a walkable tree?)
But ultimately my map would fail as it would be just that, a map, not a scenario... I have never been able to script anything so my maps would be static... But I guess that in itself is not bad, they could then be used with normal gametypes I guess...